1. Field of the Invention
The present invention relates to a power converter, and more specifically relates to a control circuit of a switching power converter.
2. Description of Related Art
Flyback power converters have been widely used to provide power supplies for electronic products, such as home appliances, computers, etc. For achieving high efficiency and reducing power loss, the power converters are normally developed to be operated in a continuous current mode (CCM) to reduce the conduction loss, particularly for being operated at a low input voltage and a high output current. However, when the power converters are operated at a high input voltage, quasi-resonance (QR) is preferred for reducing switching losses and EMI. The present invention is thus directed to a control circuit to adaptively operate the power converter at QR and in the CCM to achieve high efficiency. The detailed technologies of the flyback power converters can be found in textbooks, such as “Switchmode Power Supply Handbook” authored by Keith H. Billings and published by McGraw-Hill Book Co. on December 1989, and “Switching Power Supply Design” authored by Abraham I. Pressman and published by McGraw-Hill Book Co. on December 1991.